Preparation of a plastic for its extrusion particularly in the form of a gaged bead intended to be used as a seal and interlayer in multiple glazings

ABSTRACT

The invention relates to the distribution of a plastic of the butyl rubber type, and more particularly to its preparation and its routing from a tank where it is hard, viscous and at a relatively low temperature, to an extrusion nozzle where it must have a viscosity and a hardness much lower than those that it had initially. The invention proposes a preparation in several stages combining heating and pressurizing so as to feed, at the desired delivery and with the desired quality of plastic, an optionally mobile nozzle. The invention applies to the production of a bead that is used as a seal and as an interlayer in multiple glazings.

This is a division of application Ser. No. 06/753,608, filed July 10,1985, and now U.S. Pat. No. 4,714,425.

BACKGROUND OF THE INVENTION

This invention relates to the distribution of a plastic of the butylrubber type, particularly for the extrusion of the bead intended toserve as a seal and interlayer in multilayer glass sheets, hereinafterreferred to as multiple glazings, and it relates more particularly tothe preparation of said plastic and its routing from a tank where it ishard, viscous and at a relatively low temperature to an extrusionnozzle, optionally mobile in relation to the tank, where it should havea viscosity and hardness much lower than it had initially in the tank,and a higher temperature.

It is known from French Pat. No. 2 211 413 how to prepare a plastic ofthe butyl rubber type for the extrusion of a bead intended to bedeposited on a glass sheet to make a multiple glazing, to work fromsmall amounts of material, that can be easily and quickly heated, toobtain satisfactory characteristics of viscosity and hardness, on theone hand for the extrusion of the bead, on the other hand for thebonding of the bead thus extruded to a glass sheet. In addition,according to this prior patent, the extrusion unit is stationary and theglass sheets move to receive the extruded bead successively along alltheir edges.

This prior technique is satisfactory. However increase the rates ofproduction on the one hand, and to increase the dimensions of theextruded beads on the other hand, it has been known to avoid workingfrom small amounts of material, which would necessitate too-frequentstops for refeeding, but from large amounts of material, particularlydirectly from the drums of raw material delivered by the supplier.

These large amounts are more difficult to heat than small amounts, whichrestricts the deliveries and the rates while, on the contrary, it isdesired to increase said deliveries and said rates.

To obtain at the output of the extrusion nozzle a suitable material,with the desired delivery, at the suitable temperature, different stagesfor preparing the material therefore have to be created, whichnecessitates circuits to feed these various stages.

Further, it has also been considered to use a technique for placing thebead on the glass sheets in which the nozzle supplying the bead would nolonger be stationary, but would move, at least in one direction.Therefore, the circuits conducting raw material up to the nozzlenecessarily have a relatively great length and cannot be stationary. Toconvey the material along these circuits, it is, on the one hand, asalready stated, difficult to heat it sufficiently to lower itsviscosity, on the other hand neither is it desirable to overheat it, soas not to degrade it. It is therefore necessary during the variousstages for preparing the plastic to combine a moderate heating and apressurizing.

It is known how to convey plastics in hoses, optionally cladded, butsuch material is, at certain times in its path, at pressures greaterthan 300 bars and at temperatures greater than 100° C. and the knownhoses are incapable of resisting this temperature and this pressure atthe same time.

SUMMARY OF THE INVENTION

This invention aims to avoid the drawbacks of the prior techniques,i.e., a stationary nozzle and frequent stops for refeeding due to theuse of small amounts of basic material.

The invention contemplates making possible the distribution of a plasticat a high delivery and continuously when necessary, through at least onemobile nozzle, said plastic coming from a large-sized tank where it isavailable with a high viscosity and a high hardness, much higher than itmust have at its output through the nozzle.

For this purpose, the invention proposes a process for preparing aplastic of the type having a butyl rubber base, from a mass of saidmaterial in the raw state, having in particular a high viscosity and ahigh hardness, for its extrusion through an output nozzle, particularlyin the form of a gaged bead having a viscosity and a hardness lower thanthose of the material in the raw state. According to the invention asmall volume of the material mass is heated, material from this volumeis continuously removed by subjecting it to a pressure, this removedmaterial is put under a higher pressure to propel it up to the outputnozzle, this material is continuously introduced into a variable volumemagazine that can expand when the amount of material that it receives isgreater than the amount of material that it delivers and, on the otherhand, that can shrink under the opposite conditions, necessary amountsof material are removed from this variable volume magazine, at thedesired delivery, limited however by the volume of material stored inthe variable volume magazine and by the continuous delivery which feedssaid magazine.

The invention also proposes an installation for preparing a plastic ofthe butyl rubber type including: a tank of said material having a wall,particularly the cover, applied with pressure against the material, wallor this cover bored with an outlet orifice, having such a shape that thesection of the volume of material that it encloses is smaller the closerit is to the output orifice, and being equipped on its face orientedtoward the material with heating appendages which plunge into saidmaterial.

A pump is located at the output of the tank for supplying a continuousdelivery of plastic under a high pressure while a variable volumemagazine consists of a cylinder and a piston returned to the inside ofthe cylinder with a constant force less than the force exerted by thematerial supplying said magazine and an output nozzle is fixed to thevariable volume magazine.

According to a particular embodiment, the cover of the tank has aconical shape.

According to the invention, the variable volume magazine and the outputnozzle are able to move, said magazine and the pump then being connectedby rigid conduits joined by rotating connections.

Advantageously, a positive-displacement pump is located at the output ofthe variable volume magazine upstream from the output nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews and wherein:

FIG. 1A is a top view of the entire plastic distribution installation,

FIG. 1B is a profile view of the installation of FIG. 1A,

FIG. 2 is a more detailed view of the tank with a cone-shaped coverapplied on the material,

FIG. 3 is a view of the detail of a seal of the cover applied on thematerial,

FIG. 4 is a detailed top view of an internal gear pump located at theoutput of the tank,

FIG. 5 is a detailed view of the variable volume magazine placeddownstream from the pump according to FIG. 4 and,

FIG. 6 is a section at the rotating connections that equip the transfermeans connecting the pump of FIG. 4 to the magazine of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B provide an overall view of the installation forpreparing a plastic for supplying a bead intended to be used as a sealand an interlayer in a multiple glazing.

This bead 1 is intended to be deposited on a glass sheet 2, arrangedvertically or approximately vertically against a wall 3, particularlywith insertion of a gas cushion between said wall 3 and glass sheet 2,and resting on rollers 4 of a vertical conveyor.

The installation for preparing the plastic is mounted on a frameincluding a base 5 and a vertical panel 6 on which the various elementsof the installation rest or are fastened.

This installation includes an open topped tank 7 of raw material 8 to beprepared and to be distributed in the form of bead 1, equipped with aheated cover 9, of a particular shape detailed below, a pump 10 at theoutput of this tank 7, a variable volume magazine 11, apositive-displacement pump 12, a nozzle 13 that can be oriented, means14 of for translation of nozzle 13 and for magazine 11 in a directiondifferent from that of the movement of glass sheets 2, and in this casein a vertical direction, at right angles to the direction of movement ofglass sheets 2 and parallel to the plane of said glass sheets and ofwall 3, and means 15 for transferring the raw material from pump 10 tovariable volume magazine 11.

Tank 7 has a broadened base 16 by which it is attached to base 5 thanksto a clamp 17. This tank 7 generally consists of the drum in which theplastic, for example having a butyl rubber base, is delivered by thesupplier. As can be seen more particularly in FIG. 2, it is covered witha cover 9 able to plunge into it like a piston, under the pressure oftwo lateral jacks 18 and 19 (that also can be seen in FIG. 1A) acting onit by a gantry 20. This piston-forming cover 9 is equipped with at leasttwo ring seals 21 and 22 that rub against the walls of the drum so as toachieve fluid-tightness despite the annular corrugations that aregenerally provided on the drums. These seals 21 and 22 have an outsidediameter slightly greater than that of the inside of the drum; they aresolid, bulky, hard (Shore hardness on the order of 70°), of a continuousrubber type material, and as shown in detail in FIG. 3, they are eachfitted in a groove 23, 24 of cover 9.

Advantageously, to enable the centering of cover 9 on tank 7 and itsprogress inside said tank, both in the direction of plunging and in theopposite direction, each seal 21, 22 has a profile provided with twocants 25, 26 along an angle on the order of 20° with respect thedirection parallel to the lateral wall of tank 7 against which theyrest, separated by a flat piston for 27 whose surface is at least 1/3 ofthe total surface outside groove 23, 24 oriented toward the lateral wallof tank 7.

This piston-forming cover 9 has such a shape that it delimits a volumewhose section is smaller the closer it is to an outlet 28 of the cover.

It can have the shape of a conical surface, in particular either a coneor a pyramid depending on whether tank 7 is cylindrical or prismatic,outlet 28 being located at the tip of the cone of the pyramid.

Generally, tanks 7 are cylindrical drums and cover 9 then has a concicalshape and in particular a right circular cone.

The surface of this piston cover 9 is equipped with heating means suchas electric resistors 29.

The face directed to the inside of tank 7 further provided withappendages 30, also heated.

These appendages 30 can be of variable lengths. Preferably, they arelonger the closer they are to the outlet at the axis of the cone or ofthe pyramid that constitutes cover 9.

Advantageously, to facilitate the housing of piston cover 9 in tank 7,particularly when it arrives at the end of travel, these appendages 30are contained inside the volume delimited by said piston cover 9.

To make it possible to use all of the material contained in the drum,the bottom of said drum opposite conical cover 9, equipped with heatingappendages 30, can have a shape complementary to that of cover 9 withits appendages 30.

According to an advantageous variant, the bottom of drum 7 is flat, butit is provided with a nonadhering coating. This coating of the teflon,silicone, graphite, talc, etc. type, can be deposited directly on thebottom, or better on an intermediate bottom, for example of paper orcardboard.

Advantageously, this intermediate bottom, for example of siliconedpaper, in is the shape of a crown, and in the place of the hollowed partof the center of the crown, the nonstick coating is deposited directlyon the bottom of drum 7.

Outlet 28 through piston cover 9 of tank 7 feeds pump 10 directly.

Advantageously, considering the considerable viscosity and considerablehardness of the material having a butyl rubber base, even after theremoval from tank 7, considering the continuity of required deliveryand, of the size of the necessary delivery, a rotary internal gear pump10 is involved.

Preferably, to avoid the drawbacks due to a resistance that is too greatfor functioning, in particular at the time of starting, this pump 10 ishydraulically actuated. This pump is represented diagrammatically inFIG. 1A and shown more in detail in top view in FIG. 4.

This rotary internal gear pump 10 has a pump body 31 enclosing a toothedcircular crown 32 and, a rotor 33 also toothed, whose teeth have a shapecomplementary to the shape of those of crown 32. This rotor 33 isoff-center in relation to crown 32 due to an off-centering core 34. Thisrotor 33 is bored in its center with a housing 35 with a keying groove36 to receive a drive shaft and a locking key, not shown here, intendedto drive rotor 33 in rotation.

Teeth 37 of rotor 33 and corresponding teeth 38 of crown 32 are distantfrom one another in zone 39 which surrounds off-centering core 34 thusforming large spaces 40 between them.

Going away from this zone 39, teeth 37 and 38 are increasingly betterfitted into one another, which leads to a gradual restriction of spaces40.

Spaces 40 are almost nonexistent and teeth 37 and 38 completely fittedinto one another in zone 41 that is diametrically opposed tooff-centering core 34.

Advantageously, as can be seen in FIG. 4, teeth 37 and 38 have atrapezoidal shape, which increases their mechanical strength and makesit possible to have larger spaces 40 than with another shape of teeth,particularly triangular.

Advantageously, to make a better supercharging of spaces 40 possible bythe material removed from tank 7, the material is brought opposite saidspaces 40, in region 39 where they are the largest, above from and belowat the same time by a double pipe not shown in the figures, resultingfrom the division of a pipe 42 connected to outlet 28 through cover 9. Apump output pipe 43, that can be seen only in FIG. 1A is providedapproximately perpendicular to zone 41 where spaces 40 are the smallest.This pipe 43 goes through pump body 31 in a direction approximatelyperpendicular to the plane of crown 32 and or rotor 33. Advantageously,the mouths of the supply pipes and of evacuation pipe 43 cover severalspaces 40.

As can be seen in FIGS. 1A and 1B, the material coming from pump 10 istransmitted to the elements of the installation located downstream, bytransfer means 15 consisting of multiplicity of rigid conduits 44, 45,46 resistant to pressure and heat, connected to one another and to theupstream and downstream devices by rotating connections 47, 48, 49, 50an example of which is shown in section in FIG. 6.

This rotating connection, for example 49 FIG. 6, comprises a maleelement 51 fitted into a female element 52, each of these two elements51 and 52 being connected by welding to upstream conduit 45 anddownstream conduit 46. The fluid-tightness between these two elements 51and 52 is obtained through annular seals 53 and 54 and the rotation ofthe male part 51 in the female part 53 is facilitated by a series ofballs 55 and 56 that roll in annular grooves 57 and 58 bored partiallyin male element 51, partially in female element 52.

Advantageously, to facilitate the rolling of balls 55 and 56 on the onehand and their exchange when they are worn out on the other hand, theseballs are mounted elastically inside cavities 59, 60, on bearings 61, 62that can be removed from the outside of female element 52.

These connections with a single axis of rotation are, with regard tofluid-tightness at high pressure, preferably to ball and socketrevolving systems with multiple axes of rotation.

The movements in all the directions of the space are made possible bythe justaposition of a multiplicity of these connections having a singledegree of freedom, these connections being joined by bent rigidconduits.

Transfer means 15 described above are advantageously heated. They areintended to connect output pipe 43 of pump 10, which can progress inheight since it is fixed to piston cover 9 which plunges into tank 7, tovariable volume magazine 11 fixed to nozzle 13, which is capable ofmovements of translation in a vertical direction to be able to deposit abead 1 over the entire height of glass sheet 2. To avoid blockingconduits 45 and 46 i aligned position when piston cover 9 is in thehighest position and nozzle 13 is in lowest position or vice versa, saidconduits 45 and 46 have a length such that there always exists betweenthem an angle less than 180°.

The plastic material conveyed by transfer means 15 is introducedcontinuously at a steady delivery rates to the inside of variable volumemagazine 11. This magazine 11 can be seen in top view in FIG. 1A, inside view in FIG. 1B and in more detailed view in FIG. 5. In comprises acylinder 63 equipped with an input opening 64 and an output 65 feedingpositive-displacement pump 12. Inside this cylinder 63 can move a piston66 can move through whose entire length passes a plastic intake channel67 which opens inside cylinder 63, this channel 67 being connected onthe side of its upstream end to the last rotating connection 50 oftransfer means 15.

Piston 66 is returned to the inside of cylinde 63 by a system exerting aconstant force, particularly one or more jacks, and as in the exampleshown, two jacks 68 and 69 each connected on the one hand to cylinder 63by a flange 70 and, on the other hand to piston 66 by a plate 71. Thereturn force of jacks 68 and 69 is less than the force exerted by theplastic entering into magazine 11 to avoid any delivery counter to thenormal direction of advance. The end of piston 66 plunged into cylinder63 is equipped with annular scraping segments. End of travel stops 72,73 of piston 66 inside cylinder 63, in each of the two possibledirections of movement of said piston 66, also provided. These stops areengage contact elements 74, 75 belonging to piston 66 one element 74determining the maximum penetration position, on the rear part of thepiston, the other element 75 determining the maximum withdrawalposition, therefore the maximum volume inside of cylinder 63, on thefront end of the piston. An intermediate element 90 intended to come incontact with stop 72 is provided on the body of piston 66, this elementdetermining the low level for refilling cylinder 63 and triggering theactuation of the upstream means for supplying plastic.

Contact between stops 72 and 73 and corresponding elements 74, 75control stop the injection of plastic through output 65 and respectivelystopping the supply of material to cylinder 63.

Advantageously, to avoid cooling of the plastic and optionally tocomplete its heating so that it reaches the desired consistency, thewalls of cylinder 63 and of channel 67 are heated.

This variable volume magazine 11 delivers its plastic with a constantpressure to standard positive-displacement pump 12 whose speed ofrotation can vary on demand.

At the output of pump 12, the plastic is supplied to an extrusion head76 comprising nozzle 13. This extrusion head 76 is mounted on a carriage77 pulled by means such as jacks and an endless screw activated by anelectric motor, not shown, making is possible to move nozzle 13 close toor away from glass sheet 2. The electric motor and the endless screwmake it possible to finely adjust the advance of carriage 77 carryingnozzle 13, particularly as a function of the thickness of the glasssheets 2, while the jacks make movements of a predetermined magnitudepossible.

This extrusion head is mounted on a crown 78 that revolves around anaxis perpendicular to the plane of vertical, or approximately vertical,wall 3 so as to correctly orient nozzle 13 with regard to the glasssheets as a function of the relative direction of movement of saidnozzle and of said glass sheets. Actually, as taught in French Pat. No.2,294,313 U.S. PAT. No. 4,205,104 the nozzle should make an anglebetween 15° and 45° and preferably between 25° and 35°, with the glasssheet.

To lock crown 78 in predetermined positions, a locking punch 79 engagesin notches provided for this purpose in corwn 78 the, notches not shownin the figures.

The unit of variable volume magazine 11, positive-displacement pump 12,extrusion head 76, carriage 77 can move in translation in relation toglass sheets 2 under the action of means 14 detailed below. For thispurpose, this unit is mounted on a plate 80 that can move along twoslides 81, 82 parallel to wall 3 and therefore to the plane of glasssheets 2, in a direction different from that of the movement caused bythe vertical roller conveyor 4 and in particular in a direction at rightangles to the one imparted to glass sheets 2 by this roller conveyor 4.The movement along these two slides 81, 82 is caused by a motor 83 whichdrives in rotation an endless screw 84 parallel to slides 81 and 82,this endless screw 84 being engaged in ball sockets not shown, fixed toplate 80. Slides 81 and 82 and endless screw 84 are fastened alongvertical panel 6.

As known in the art, nozzle 13 is also equipped with a system foradjusting the height of extruded bead 1, and with a bead cutter, notshown.

Also as is known in the art according to the French Pat. No. 2,207,799,a system known in the art able to create a partial vacuum in the circuitfor supplying plastic has a bypass connection immediately upstream fromnozzle 13. This system is also not shown in the figures.

The previously described installation operates in the following manner:

Plastic 8, for example, having a butyl rubber base, is provided in adrum 7. This drum is fastened on base 5 by clamp 17 which grips its base16. Cone-shaped cover 9 is placed on this drum, then pressed against thematerial which is contained there by jacks 18 and 19. Under the actionof this pressure and also the heating produced by heating appendages 30and by the wall of this conical piston, the material covered by pistoncover 9 is gradually softened and removed from drum 7 through output 28.The pressure under which the plastic is removed, however, isinsufficient to convey it through the entire distribution circuit tooutput nozzle 13. However, this pressure is sufficient to superchargepump 10, especially as the supercharging can be done on both faces ofpump 10 by the two supply pipes. Because of this double supply, becauseof the particular shape of its teeth, this pump can deliver into itsoutput pipe 43 a steady delivery of plastic under a pressure much higherthan that upstream of said pump.

This pressure in the output pipe can be on the order of 300 of 350 bars.Thanks to this high pressure, it is not necessary to overhear thematerial to convey it up to nozzle 13, and therefore it is not likely tobe degraded.

At the output of this pump 10, the plastic under high pressure, howeverat a temperature on the order of 100° C. is introduced into the conduitsand the rotating connections of the transfer system 15. Thanks to thistransfer system 15, generally of steel, the high pressures, and therelatively high temperature, can be supported without leaks.

The multiplicity of rigis conduits 44, 45, 56 and of rotatingconnections 47, 48, 49, 50, despite the single degree of freedom of eachof said connections, makes it possible to transfer the plastic from pump10, which descends strictly vertically into drum 7, to variable volumemagazine 11 which also progresses, along slides 81, 82 in a slightlydifferent direction, i.e., generally inclined about 5° in relation tothe vertical. Thus, thanks to these possible movements, conduit 46 androtating connection 50 can take the position indicated in broken linesin FIG. 1B, to feed nozzle 13 located toward the top of glass sheet 2 asshown in broken lines in this same figure.

Regardless of the relative positions of piston cover 9 and of nozzle 13or of variable volume magazine 11, the routing of material 8 alwaystakes place and under the same conditions.

Magazine 11 is therefore continuously fed with a delivery, sometimeshowever too small to extrude continuously certain very large beads 1, onthe order of 15 mm and more, on large-sized glass sheets 2, that canhave perimeters of close to 15 m. Thanks to magazine 11, an intermediatereserve of material can be constituted in particular by taking advantageof the stops for extrusion through nozzle 13, between two glass sheets 2or further at the corners of said glass sheets. During these breaks,piston 66 moves out of cylinder 63 thus increasing the capacity ofmagazine 11.

On the other hand, during the extrusion of a bead of great height and ingeneral of great section, if the continuous delivery provided by conicalheating piston 9 and rotary internal gear pmp 10 is less than thedelivery coming out through nozzle 13, the necessary additional deliveryis obtained by gradually emptying the reserve in magazine 11. In thiscase, piston 66 advances, on the contrary, to the inside of cylinder 63.Thus, for example, when making a bead 1 of considerable height, 2.8 kgof material per minute is needed, thanks to the reserve accumulated inthe variable volume magazine, it is possible to get by with a supply ofmaterial by conical heating piston 9 and gear pump 10, continuously, of1.3 kg per minute. This variable volume magazine 11 also makes possible,by the action of lateral jacks 68 and 69 to control the pressure of theplastic, a control which is particularly important for the feeding ofpositive-displacement pump 12.

Positive-displacement pump 12 whose output delivery is regulated byacting on the motor which controls it, supplies the plastic at thedesired delivery for the extrusion of a bead of determined section.Extrusion nozzle 13 is positioned directly opposite glass sheets 2, at adistance therefrom and oriented in the direction of the relativemovement of nozzle 13 and of glass sheet 2. Once nozzle 13 is correctlyoriented by rotatin of crown 78 which carries it, punch 79 locks saidcrown.

If bead 1 must be deposited along a ling parallel to the direction ofmovement provided by roller conveyor 4, nozzle 13 remains stationary,and extrudes the bead while the glass sheet passes before it.

If, on the other hand, bead 1 must be deposited along a long parallel toslides 81, 82, roller conveyor 4 remains at the stop and plate 80 movessteadily, under the action of motor 83 acting on endless screw 84 and onthe ball sockets. The nozzle is thus driven with a steady movement oftranslation and it deposits bead 1 on immobile glass sheet 2.

By simultaneously guiding the movement of plate 80 and that of rollerconveyor 4, a depositing of the bead along lines other than vertical andhorizontal can also be obtained.

Therefore, thanks to this installation for preparing a plastic, therecan be continuously obtained using several combined stages, at theoutput of an optionally mobile nozzle 13, a bead 1 of said plastic at adesired temperature, delivery, pressure, viscosity and hardness while atthe beginning of the installation the material is at a much lowertemperature, the viscosity and the hardness are much higher, whereas asingle heating would be as much too long to soften the initial materialaccording to the desired consistency and, moveover, would even be likelyto degrade said material.

When the material contained in drum 7 is used up, conical cover 9equipped with heating appendages 30 is withdrawn from drum 7. In thecase of a drum bottom provided with a nonstick coating, a certain amountof plastic, that is tobe superposed on the material in the new drum, iswithdrawn at the same time inside the conical cover, which makes itpossible to restart the injection immediately and which avoids purging.

Obviously, numerous modificatons and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

I claim:
 1. An installation for preparing a plastic material of the typehaving a butyl rubber base, comprising:a tank having an open top andcontaining raw plastic material; a cover inserted in said open top, saidcover having an outlet orifice, a face of said cover oriented towardssaid plastic material having a shape such that a sectional area of avolume of the plastic material enclosed by said cover is smaller thecloser said plastic material is to said outlet orifice; means forheating said cover; means for pressing said cover for movement into saidtank, whereby the plastic material in said tank is heated and forcedthrough said outlet; and a plurality of heating appendages formed onsaid face of said cover and extending toward said plastic material,wherein said appendages extend parallel to a direction of movement ofsaid cover, and wherein the length of said appendages increases ininverse correspondence with the distance of said appendages from saidoutlet, whereby said heating appendages closest to said outlet provideincreased heat transfer surface area to the plastic material as comparedto ones of said heating appendages further from said outlet.
 2. Theinstallation of claim 1 wherein said face of said cover forms a cone. 3.The installation of claim 1 wherein said face of said cover ispyramidal.
 4. The installation of claim 1 wherein said appendages arepositioned entirely within a volume delimited by said cover.
 5. Theinstallation of claim 4 wherein the bottom of said tank has a shapecomplementary to that of said cover and said appendages.
 6. Theinstallation of claim 1 wherein said means for pressing comprise jacksextending between said cover and a base to which said tank is mounted.7. The installation of claim 1 including a pump in said outlet.
 8. Theinstallation of claim 1 including sealing means between said cover andsaid tank.